Hello josephine shirley,
By default the TabControl stretches to fill the Container's size. (no Width/Height or any Alignment property should be set). You can use for example Margin to have an ofset from the Container.
If you need more complicated scenario - you can bind the Width and Height proeprties of the tab to the named container's (using ElementName binding) Widht and Height proeprties and have custom logic in Converter for example.
If you give us more details we can create example for you.
Hope this will help you.
All the best,
the Telerik team
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